1. Field of the Invention
This invention relates to a microwave apparatus for controlled tissue ablation. It relates especially to such apparatus which incorporates a minimally invasive microwave antenna catheter which can transmit and receive signals at different frequencies.
It is well known in the medical field to transmit electromagnetic energy to internal tissue by way of an antenna placed close to the tissue in order to heat the tissue sufficiently to ablate or necrose same by hyperthermia. Invariably the antenna is incorporated into a catheter which can be inserted into the body and positioned near the tissue of interest. In many cases, catheter ablation of tissue is the preferred treatment for cardiac arrhythmia.
2. Description of the Prior Art
Heretofore, various antenna types have been used for ablation/necrosis treatment applications. These include monopole, dipole and helical antennas as well as capacitor tip antennas. See, for example, my U.S. Pat. Nos. 4,583,556, 5,683,382 and 6,932,776. Although those prior antennas and the apparatus associated therewith are certainly capable of heating tissue, they are not particularly suitable for carrying out minimally invasive procedures such as the ablation of heart tissue. This is because the prior antennas are relatively large and stiff making it difficult to place the antenna in the position necessary to treat the problem of cardiac arrhythmias. Such treatment usually requires that the antenna be placed close to one of the major blood vessels where it connects to the heart and to deliver a uniform, predictable and controllable heating pattern to ablate or necrose tissue in the vessel wall that will produce a lesion of just the right size to treat the arrhythmias.
Also, the antenna catheters commonly used for this purpose do not monitor the actual temperature of the tissue being heated by the catheter. At most, they may incorporate a thermister or thermocouple in the catheter tip that is used to control the output of the transmitter that produces the microwave energy radiated by the antenna. However, those devices simply sense the temperature at the catheter, not the actual temperature of the tissue being treated. This can result in the tissue being underheated in which case the procedure will take longer than it should, or being overheated resulting in unintended damage to the tissue adjacent to the desired lesion.